Browse Forums Building Standards; Getting It Right! 1 Apr 01, 2022 9:31 am I have a problem with gutters overflowing back into the eaves and inside walls of a recent build. The builder is making some rectification, which includes additional overflowing provisions. However, the area of the house in question is only 1.2m away from surrounding concrete driveways and neighbours garage, so frequent overflowing is not desirable for my slab. So, I would like to monitor for gutter overflow, and then check whether the rainfall event exceeded my the 1:20 ARI for my region. I've had a look all around the BOM website and found some very interesting information, but could not find a way to get the 1:20 ARI for my region. Could someone point me to it? Also, is there anything on the BOM that will give me the peak 5 minute rainfall for the previous day? I'm located in Mount Waverley, Melbourne. Many thanks. Re: Monitoring for gutter overflow - how do I find my 1:20 A 2Apr 01, 2022 10:54 am AS/NZS 3500.3 use to deem your area's 1:20 ARI to be 130 mm/hr, based on an average rain intensity of 2.166 mm per minute over a 5 minute duration. There is a swing towards using more area specific calculations, the Intensity Frequency Duration (IFD) found on the BOM site being one but from memory that might now be out of date. Not sure on that. Victoria has a variation in the National Construction Code (NCC) that removes the BCA (Part 2 of the NCC) as a deemed to satisfy requirement for roof drainage installations. Only the superior Australian Standards referred to in the NCC are required. In fact, Victoria has, at no time, adopted the BCA as a Deemed To Satisfy (DTS) provision for roof drainage systems. The Plumbing Regulations 2008 adopted the Plumbing Code of Australia (PCA) in 2008. The PCA at the time of adoption (2004 edition) made no reference to the BCA under the DTS provision for roof drainage systems. On May 1 2011, the PCA was introduced into the NCC as Volume 3. It was at this time that Victoria introduced the variation into the NCC to exclude the BCA as a roof drainage provision. It is my experience that gutter overflows on Victorian houses are nearly always caused by non adherence to compliance and you should have someone well versed in the art check your roof drainage for AS compliance. If your house has the usual 22.5 degree roof pitch, the roof plan (roof space) area is multiplied by 1.21 to arrive at the roof catchment area which factors wind driven rain. If you also have the standard 115mm quad gutters, your factored roof areas draining to each downpipe should be a maximum of about 47 sq m. Even when gutters overflow, water should not drain back into the eaves and inside walls. Have you checked how high the gutters are mounted on the fascia?. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Monitoring for gutter overflow - how do I find my 1:20 A 3Apr 01, 2022 12:02 pm Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅
Wow, thank you for that information. The gutters are approx 110 x 48. There's no gap between gutter and fascia, though there are small slots on the front. I was just measuring things and found that the slots are about 1 to 2mm above the back of the gutter, and the top of the fascia is only 8mm above the back of the gutter. So only 6mm safety margin(!!). On this side of the house we have a second story roof dumping onto lower roof with small spreader. I can imagine with the volume from the 2nd story concentrated on maybe 600mm of lower roof gutter, there'd be enough sloshing around to easily overcome that 6mm. On top of that the slots are quite small and probably don't let water out quickly enough. The builder said he'd add a downpipe, and install a reverse pop for additional overflow. I'm trying to figure out how I can monitor it to make sure this overflow pop doesn't just convert the gutter problem to a slab heave problem. So if the 1:20 regulation doesn't apply, are there any rules about frequency of gutters overflowing for Victoria? Re: Monitoring for gutter overflow - how do I find my 1:20 A 4Apr 01, 2022 1:15 pm I'm about to go out, will reply properly later but there is a compliance issue. You have mentioned a "builder", is this a new house??? 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Monitoring for gutter overflow - how do I find my 1:20 A 7Apr 07, 2022 1:40 am Eaves gutter drainage compliance is calculated to cope with a 1:20 ARI but gutters can still overflow due to poor design. Spreaders diverting water to the end of a gutter when the downpipe is fitted elsewhere is one example of really bad design but compliance does not guarantee good design. Unfortunately, non compliance is also common. AS/NZS 3500.3 2018 edition replaced the 2015 edition on May 1 2018. Given your house is 2 years old, I assume that 3500.3 2018 was probably referenced but maybe the 2015 edition applied due to build time etc. Regardless, the lower gutter had to be sized to account for roof drainage from the upper and lower roofs as well as the abutting wall. As per previous advice, if your roof pitch is the standard 22.5 degrees and the gutter cross sectional area is let's say 5,200 sq mm as per the manufacturer’s specifications, the maximum factored roof harvest area is about 47 sq m. This equates to the upper and lower roof plan areas plus a calculation for the abutting wall as being a total of about 39 sq m as there is a multiplier of 1.21 for the roof pitch. The two roof areas (plus the abutting wall to allow for wind driven rain) would have to be very small to meet compliance. Another thing is the distance between the top of the gutter’s back wall and the top of the fascia. This is calculated by a hf (height freeboard) formula found in AS/NZS 3500.3 that factors the flow in the gutter. Having the top of the back wall 8 mm below the top of the fascia is not compliant. The slot’s height should not be above the back wall. Are they this level all along the gutter or just at the end? The gutter’s stop end appears to be unusually highly sloped. Is the white plastic tab in the end plate hiding a screw that forces the front of the gutter higher in that section and is there flashing between the tiles and the wall? An additional downpipe at the end would probably fix the drainage problem but is there a subsurface storm water pipe in that area? I hope so in order to avoid a lot of mess. Regardless, the installation is unprofessional and requires more work than just fitting a downpipe. The reverse pop the builder has referred to will be a 50mm inverted nozzle that drains to atmosphere. There would be no need for one if an extra downpipe is fitted. Eaves gutter roof drainage compliance states that there must be an overflow provision designed for a 1:100 year ARI. I’m not sure whether AS/NZS 3500.3 2018 recognised overflow slots as a deemed to satisfy overflow provision but the 2015 edition never and the new 2021 edition (comes into effect in September 2022) doesn’t. A call to the VBA will answer this Q for you. If slots were not recognised in the edition applicable to your build, then the builder needed to have it included as a certified Performance Solution but the gutter is not correctly installed in any case which makes that point moot. The BOM use to list all weather stations and I assume they still do but I doubt there would be a record of a regions 1:20 ARI event as it is taken over a 5 minute period. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Much a do about nothing. You can see the fall heading to the actual drains. Stormwater ingress will be minimal and it's far better to have the top sitting flush rather… 12 6259 Thanks for that, the PVC pipe is still about 40cm below ground level and it sticks out of the sand with no end cap or anything on it just open pipe, is this the finished… 2 10480 No, I even have sections of narrowness where the tiles won't slide up any further. When I manage some spare time, I might play around with the first DIY part of my… 7 4943 |